Carpet backing, roofing membranes and other products commonly require the use of flexible, yet tough and durable fabrics. In the past, such fabrics have typically been made of woven and nonwoven natural artificial fabrics such as hemp, jute, nylon, polyester, and the like. When used as carpet backing, the fabrics are commonly coated with latex or similar material, and when used as roofing membranes the fabrics may be coated with bituminous material.
Some of these fabrics may assume composite constructions. For instance, many roofing membranes include a layer of woven material and a layer of nonwoven material. The woven material typically provides strength and durability. The nonwoven material prevents bitumen bleed-through in roofing membranes and adhesive from falling through the carpet backing during carpet manufacture. Some manufacturers glue the nonwoven material to the woven material. However, adhesive bond failure occurs in a high percentage of such products. Others have overcome this problem by stitching or knitting the nonwoven material to the woven material.
U.S. Pat. Nos. 5,474,838 and 5,569,430, for example, describe roofing membranes, including reinforcement material consisting of a fiberglass scrim fabric to which is stitched or knitted a layer of nonwoven thermoplastic staple fibers formed from polyester and/or nylon. The nonwoven material is stitched or knitted to the fiberglass scrim on a Malimo or weft insertion machine with stitch through capability. The composite fabric is then saturated with bituminous material to produce the final roofing membrane product. A composite reinforcement material so constructed results in a structurally "imbalanced" fabric. The shortcomings of such a construction become increasingly pronounced as the weight of the nonwoven material increases and the reinforcement is exposed to elevated temperatures, e.g., when the reinforcement is saturated with hot bituminous material in the final stage of the roofing membrane manufacturing process.
Additionally, when the saturated roofing membrane is installed on a roof, the roof may be covered with a hot bituminous tack coat prior to placement of the membrane. Once the membrane is placed, heat and/or a second coating of hot bituminous material may be applied to the upper surface of the membrane. If the nonwoven material in the composite fabric is sufficiently heavy in weight and exposed to sufficiently hot bitumen, however, the thermoplastic nonwoven material may shrink somewhat, whereas the fiberglass scrim remains essentially constant in size. The differential shrinkage of the nonwoven material relative to the scrim may cause the membrane to curl or otherwise deform in either or both of the warp and weft directions of the membrane. As a consequence, roofing membranes constructed according to those described in U.S. Pat. Nos. 5,474,838 and 5,569,430 may produce a less than desirable aesthetic effect when applied to a roof surface. Even more significantly, they may not uniformly adhere to the roof thereby creating gaps which may permit possible ingress of water, dirt, pollutants and other atmospherically-borne matter that may be harmful to the roof structure.
An advantage exists, therefore, for a composite fabric suitable for roofing membranes, carpet backing and other applications which is lightweight, high-strength, balanced in construction and resistant to deformation when exposed to elevated temperatures.